The present invention relates to input/output channel and networking systems, and more particularly to methods of using a Fibre Channel fabric or intelligent bridging hub to interconnect Fibre Channel Arbitrated Loops composed of private loop devices (i.e., devices which do not support direct fabric attachment).
Fibre Channel is an American National Standards Institute (ANSI) set of standards which describes a high performance serial transmission protocol which supports higher level storage and network protocols such as HIPPI, SCSI, IP, ATM and others. Fibre Channel was created to merge the advantages of channel technology with network technology to create a new I/O interface which meets the requirements of both channel and network users. Channel technology is usually implemented by I/O systems in a closed, structured and predictable environment, whereas network technology usually refers to an open, unstructured and unpredictable environment.
Advantages of Fibre Channel typically include the following. First, it achieves high performance, which is a critical in opening the bandwidth limitations of current computer to storage and computer to computer interfaces at speeds up to 1 gigabit per second or faster. Second, utilizing fiber optic technology, Fibre Channel can overcome traditional I/O channel distance limitations and interconnect devices over distances of 6 miles at gigabit speeds. Third, it is high level protocol independent, enabling Fibre Channel to transport a wide variety of protocols over the same media. Fourth, Fibre Channel uses fiber optic technology which has a very low noise properties. Finally, cabling is simple in that Fibre Channel typically replaces bulky copper cables with small lightweight fiber optic cables.
Fibre Channel supports three different topologies: point-to-point, Arbitrated Loop and fabric attached. The point-to-point topology attaches two devices directly. The Arbitrated Loop topology attaches devices in a loop. The fabric attached topology attaches a device directly to a fabric.
The Arbitrated Loop topology was initially designed to provide a lower cost interconnect than fabrics and to provide more interconnect than point-to-point topologies. The Arbitrated Loop topology was created by separating the transmit and receive fibers associated with each loop port and connecting the transmit output of one loop port to the receive input of the next loop port. Typically, characteristics of the Arbitrated Loop topology include: first it, allows up to 126 participating node ports and one participating fabric port to communicate, second, each node port implements a route filtering algorithm, and third, all ports on a single loop have the same upper 16 bits of the 24-bit NL_Port address identifier.
There are two classifications of devices on an Arbitrated Loop: private loop devices and public loop devices. Public loop devices attempt a Fabric Login (FLOGI) upon initialization. Public loop devices also are cognizant of all twenty four bits of the 24-bit NL_Port native port address identifier. Public loop devices will open the fabric port at Arbitrated Loop Physical Address (ALPA, bits 7 to 0) zero when the domain and area (bits 23 to 8) do not match their domain and area. Private loop devices use only the lower eight bits of the ALPA and can only communicate within the local loop.
Generally, the disadvantages of the Arbitrated Loop topology include: first, it is a blocking topology, that is, only a single connection between a pair of nodes is allowed at any point in time (excluding the broadcast mode). Second, device buffering occurs in each device as it has a six word buffer, creating a delay of up to 225 nanoseconds. This delay is additive with each device in the loop. The delay creates overhead for the communicating devices when a large number of devices are connected to a loop. Third, distance also adds delay to a loop and is additive for each device. For copper medium there is a 4 nanosecond delay per meter and for optical medium there is a 5 nanosecond delay per meter. Fourth, robustness is an issue since all devices are on one loop any device failure will cause the entire loop to fail or reset. Fifth, the total bandwidth available is limited to the bandwidth of the loop itself. Finally, device failure is an issue since while frames are being transmitted, a timeout in an upper level protocol may occur, thereby disrupting the applications.
Loop devices are typically interconnected on an Arbitrated Loop with a hub, see FIG. 22 numeral 678. The hub is a passive device, that is a loop exists within the hub 674, 675, 676, 677, 679. A hub in most cases maintains the loop""s integrity when devices are removed, powered off, or fail by using a port bypass circuit 674, 675, 676, 677. Hubs simply receive and redrive the signals to individual devices.
There are many disadvantages which result when interconnecting private loop devices with hubs: First, hubs do not address the blocking nature of the loop topology. Second, jitter is propagated from bypassed nodes. This additive affect causes loop instability when a large number of devices are interconnected. Third, when data is currently being transferred and a device attached to a hub is powered off or fails, the loop could be reset which is destructive to the communicating devices. Fourth, if a device is inserted into a live loop the loop will be reset which is destructive to the communicating devices.
The majority of initial Fibre Channel equipment deployment utilizes the Arbitrated Loop topology with hubs as the interconnect. These environments are experiencing all the previously defined problems inherent in both Arbitrated Loop topology and with hub deployment. The blocking nature of the Arbitrated Loop is limiting the number of devices on a loop. The distance and delay parameters are also creating more overhead for the loop. Finally the loop is being reset by single devices.
As such, it is the goal of this invention to provide apparatus and methods which solve or mitigate these problems.
This invention relates to methods and apparatus for Fibre Channel interconnection of a plurality of private loop devices through a Fibre Channel private loop device interconnect system. In the preferred embodiments, the Fibre Channel private loop device interconnect system is a fabric or an intelligent bridging hub. Through these methods and apparatus, multiple Fibre Channel Arbitrated Loops, the loops containing one or more private loop devices, may be interconnected even though on separate Arbitrated Loops.
In the preferred embodiment, an interconnection system is provided for connecting a plurality of physically separate Fibre Channel Arbitrated Loops, the loops either containing, or being adapted to contain, one or more private loop devices. The apparatus preferably includes at least a first Arbitrated Loop containing, or adapted to contain, one or more private loop devices, and at least a second Arbitrated Loop, either containing, or adapted to contain, one or more private loop devices. The Arbitrated Loops are interconnected via a Fibre Channel private loop device interconnect system which is disposed between the Arbitrated Loops.
In one embodiment, a Fibre Channel fabric is disposed between the Arbitrated Loops, and includes a routing filter which filters incoming Arbitrated Loop physical addresses (ALPAs) to determine which Fibre Channel frames must attempt to be routed through the fabric. Thus, by disposing routing information regarding private loop devices within the Fibre Channel private loop device interconnect system, multiple Arbitrated Loops containing private loop devices may be interconnected.
Any type of private loop device, consistent with the apparatus and methods stated herein, may be utilized in conjunction with this system. Examples of private loop devices include storage devices, such as tape drives, JBODs and RAID subsystems, host systems, and other connections within a system, such as bridges, particularly SCSI to Fibre Channel bridges, routers, particularly Fibre Channel to asychronous transfer mode systems and Fibre Channel to ethernet systems.
Various interconnection topologies may be utilized with these systems. Beyond a single fabric having two Arbitrated Loops, any number of Arbitrated Loops may be utilized, consistent with the size constraints of the fabric. Alternately, a first fabric, with at least one Arbitrated Loop attached, and a second fabric, with at least one Arbitrated Loop, may have the first fabric and second fabric directly connected. Alternatively, or additionally, a first fabric and a third fabric, each having at least one Arbitrated Loop, may be connected through a second fabric. Yet another topology includes a first fabric having M ports, where one port is connected to storage, preferably JBODs, and the remaining Mxe2x88x921 ports of the first fabric are connected to Mxe2x88x921 second fabrics. An alternative interconnect topology includes a first fabric with M ports, and M second fabrics, each second fabric being connected to the first fabric. In yet another interconnect topology, a device is connected to a first fabric by a first path and to a second fabric by a second, independent path. In yet another interconnect topology, a first set of fabrics and a second set of fabrics may be interconnected through a first intermediate fabric and a second intermediate fabric, each of the first sets of fabrics connected to the first intermediate fabric, and separately to the second intermediate fabric, and each of the second set of fabrics connected to the first intermediate fabric and separately to the second intermediate fabric.
In yet another aspect of this invention, a method is provided for implementing a logical loop of private loop devices in a novel manner. The method generally comprises the steps of segmenting the logical loop of private loop devices into a plurality of sets, assigning each set to a physical Arbitrated Loop and connecting the Arbitrated Loops to a Fibre Channel private loop device interconnect system to effect interconnection of the Arbitrated Loops.
In another aspect of this invention, a method is provided for selectively filtering Fibre Channel frames. This method serves to route frames between one or more private loop devices on a first Arbitrated Loop and one or more private loop devices on at least a second Arbitrated Loop. Preferably, the method includes the steps of receiving the Fibre Channel frames over the first Arbitrated Loop at a connected port of a Fibre Channel private loop device interconnect system and filtering the frame by, either, forwarding the frame on the first Arbitrated Loop if the frame has an address on the first Arbitrated Loop, or, providing an xe2x80x9copenxe2x80x9d response on the first Arbitrated Loop if the address is not on the first Arbitrated Loop. Optionally, in the event that the frame includes an address not on the first Arbitrated Loop, the additional step of attempting to route the frame through the Fibre Channel private loop device interconnect system may be made. In yet another optional step, buffering of the frames destined to private loop devices not on the first Arbitrated Loop may be performed, most preferably, permitting cut-through if the route can be made without substantial buffering.
Yet another novel method of these inventions is a method for restricting attached devices to Arbitrated Loop physical addresses (ALPAs) within certain ranges. Through this method, multiple Fibre Channel Arbitrated Loops of private loop devices are configured, each private loop device on the Arbitrated Loop having an Arbitrated Loop physical address. Generally, the steps in the preferred method comprise, first, dividing the ALPAs into nonoverlapping sets, second, assigning each set to a separate physical Arbitrated Loop, and thereafter, during loop initialization, forcing the attached private loop devices to choose from the assigned set.
Yet another novel method comprises a method for resetting hosts within a Fibre Channel interconnection system of private loop devices. In this method of operation of an interconnection system, the system including more than one Arbitrated Loop, at least one loop being adapted to contain storage and one loop adapted to contain a host, those devices being private loop devices, the loops being connected to a Fibre Channel private loop device interconnect system, the method generally comprises the steps of, first, detecting at least the addition of a storage device to a first Arbitrated Loop, and thereafter, resetting the Arbitrated Loop or loops on which a host or hosts reside upon such detected addition. In this manner, a host resident on an Arbitrated Loop becomes aware of storage private loop devices which have been added to other Arbitrated Loops separated from the host bearing Arbitrated Loop by a Fibre Channel private loop device interconnect system.
In yet another method of operation of the inventive system, a method for operation with use of SCSI initiators is provided. In this interconnection system, the system includes more than one Arbitrated Loop, at least one loop adapted to contain storage and one loop containing a host, the devices attached to the loops being private loop devices, the loops being connected to a Fibre Channel private loop device interconnect system. The method generally comprises the steps of first, receiving port login (PLOGI) input/output (I/O) probes at the Fibre Channel private loop device interconnect system, thereafter, performing address look-up for the received PLOGI I/O probes, and, if a match exists in the look up, routing the PLOGI I/O probes from the Fibre Channel SCSI initiator to private loop devices on the Fibre Channel private loop device interconnect system or other Fibre Channel private loop device interconnect system. In the event that no match is found upon address look up, the PLOGI I/O probes are routed to the Fibre Channel private loop device interconnect system controller, and a link service reject (LS_RJT) is returned. Similarly, a link service reject is returned in the event that an address match is found, but where no device with the destination ALPA exists on the Arbitrated Loop corresponding to the destination.
An intelligent bridging hub adapted to interconnect a plurality of Arbitrated Loops containing private loop devices is provided. The intelligent bridging hub includes at least first and second hub submodules, the submodules comprising a plurality of ports, the ports including port bypass circuits connected to the ports for connecting to the Arbitrated Loops adapted to contain private loop devices, and, an Arbitrated Loop physical address filtering port, a router, the router being disposed between the first and second hub submodules, and a processor control coupled to the router and the first and second submodules. The router need not support all classes of Fibre Channel connections, for example, the router may optionally not support class 1 connections. Optionally, the processor control need not provide back-up route determination mechanisms.
Accordingly, it is an object of this invention to interconnect separate Arbitrated Loops of private loop devices through Fibre Channel private loop device interconnect system.
It is yet a further object of this invention to segment one logical loop composed of private loop devices into several physical Arbitrated Loops each of which is connected to Fibre Channel private loop device interconnect system.
It is yet a further object of this invention to connect private loop devices over a fabric without any a priori knowledge by those devices or special software driver modifications to support the Fibre Channel private loop device interconnect system.
It is yet a further object of this invention to route the I/O probes from a Fibre Channel SCSI Initiator to private loop devices on other ports on the Fibre Channel private loop device interconnect system or on other ports on connected Fibre Channel private loop device interconnect systems.
It is yet a further object of this invention to handle I/O probes from Fibre Channel SCSI Initiators which are destined for nonexistent devices.
It is yet a further object of this invention to filter the frames received by a Fibre Channel private loop device interconnect system port and select those frames which are destined to private loop devices on separate fabric ports or for other ports on connected Fibre Channel private loop device interconnect system.
It is yet a further object of this invention to reset private loop hosts when storage devices are added or removed on other ports on the Fibre Channel private loop device interconnect system or on other ports on connected Fibre Channel private loop device interconnect system.
It is yet a further object of this invention to limit the ALPA range that connected private loop devices can choose when connected to a Fibre Channel private loop device interconnect system port.